Search Results (4)

Two ichnofacies have been named to encompass inland eolian depositional systems, the Octopodichnus and the Entradichnus ichnofacies, and are often combined into a single, Octopodichnus–Entradichnus ichnofacies. In contrast, coastal dune fields are characterized by a mixture of traces produced by marine and nonmarine organisms attributed to a single, Psilonichnus ichnofacies. However, inland eolian depositional systems lack marine organisms and encompass multiple lithofacies, the most extensive and broadly defined as being dunal and interdunal (includes many water laid deposits). The two lithofacies host generally different ichnoassemblages. Dunes are dominated by arthropod and tetrapod walking traces, whereas interdunes are dominated by shallow burrows, though there is some overlap in the ichnoassemblages of both lithofacies. A re-evaluation of the three ichnotaxa unique to the Entradichnus ichnofacies indicates they are invalid: Entradichnus = Taenidium, Pustulichnus = Skolithos, and Digitichnus is not based on a biogenic structure. The Entradichnus ichnofacies is characterized by abundant horizontal, backfilled traces of mobile deposit feeders and other ichnotaxa that indicate it is a synonym of the Scoyenia ichnofacies. I advocate subsuming the Laoporus, Brasilichnium, and Chelichnus ichnofacies of earlier workers under the Octopodichnus ichnofacies. Thus, the two principal ichnofacies of eolian depositional systems are the Octopodichnus and Scoyenia ichnofacies, though several other ichnofacies have been identified. No single ichnofacies characterizes eolian depositional systems. Full article

Field investigations in the northwestern segment of the Greater Caucasus, a Late Cenozoic orogen, have permitted the establishment of two new geosites, namely the Ubin and Bezeps geosites. Both represent Berriasian–Middle Valanginian (Early Cretaceous) marine deposits with abundant trace fossils. The latter are attributed to the Nereites ichnofacies and indicate on deep marine palaeoenvironments (this interpretation challenges previous reconstructions). The geosites represent the palaeogeographical type of geoheritage. They are characterized, particularly, by high scientific and aesthetic importance, but restricted accessibility. Further geoheritage inventory in the central Northwestern Caucasus seems to be promising. Full article

Multidisciplinary studies have allowed us to describe the abiotic landscapes and, thus, reveal the ichnological and benthic foraminifera trends in a deep-water gateway. Mesoscale landscape mapping is presented based on the bathymetric position index, substrate types and near-bottom water temperature. Four sediment cores, retrieved from the entrance, centre and exit of the gap, were subject to computed tomography, ichnological and benthic foraminifera studies. A high diversity of abiotic landscapes in the relatively small area of Discovery Gap is detected and its landscape is characterized by 23 landscape types. The most heterogeneous abiotic factor is a topography that is associated with sediment patchiness and substrate variability. The ichnological and tomographical studies of the sediment cores demonstrate lateral and temporal differences in the macrobenthic tracemaker behaviour. The ichnofossils assemblage of the sediment core can be assigned to the Zoophycos ichnofacies with a higher presence of Zoophycos in the entrance site of the gap and during glacial intervals. Higher benthic foraminifera diversity and species richness during the Holocene are also registered in the southern part of the gap compared to the northern part. The spatial and temporal differences in macro-benthos behavior and benthic foraminifera distribution in the deep-water gateway are proposed to relate to the topographical variations of the Antarctic Bottom Water and its influence on the hydrodynamic regime, nutrient transport, etc. Full article

The distinction between turbidites, contourites and hemipelagites in modern and ancient deep-water systems has long been a matter of controversy. This is partly because the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap. In addition, the three facies types commonly occur within interbedded sequences of continental margin deposits. The nature of these end-member processes and their physical parameters are becoming much better known and are summarised here briefly. Good progress has also been made over the past decade in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics are summarised here in terms of standard facies models and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. A three-scale approach to distinction for all deep-water facies types should be attempted wherever possible, including large-scale (oceanographic and tectonic setting), regional-scale (architecture and association) and small-scale (sediment facies) observations. Full article